A Comprehensive Study of the X‐Ray Bursts from the Magnetar Candidate 1E 2259+586

Abstract

We present a statisticalanalysis of the X-ray bursts observed from the 2002 June 18 outburstof the anomalous X-ray pulsar (AXP) 1E 2259+586, observed with theProportional Counter Array (PCA) aboard the Rossi X-Ray Timing Explorer. Weshow that the properties of these bursts are similar to those ofsoft gamma repeaters (SGRs). We find the following similarities: theburst durations follow a lognormal distribution that peaks at 99 ms,the differential burst fluence distribution is well described by apower law of index -1.7, the burst fluences are positively correlatedwith the burst durations, the distribution of waiting times is welldescribed by a log normal distribution of mean 47 s, and the bursts aregenerally asymmetric, with shorter rise than fall times. However, we findseveral quantitative differences between the AXP and SGR bursts.Specifically, the AXP bursts we observed exhibit a wider range ofdurations, the correlation between burst fluence and duration is flatterthan for SGRs, the observed AXP bursts are on average less energeticthan observed SGR bursts, and the more energetic AXP bursts havethe hardest spectra-the opposite of what is seen for SGRs. Unlikethe case of SGRs, we find a correlation of burst phase with pulsedintensity. We conclude that the bursts are sufficiently similar that AXPsand SGRs can be considered united as a source class, yet there aresome interesting differences that may help determine what physicallydifferentiates the two closely related manifestations of neutron stars.